Facebook's bumpy IPO debut could signal the end of a collective hallucination. Most of it pertains to the company's ability to deliver an effective advertising machine.

Pre-IPO numbers looked nice, especially when compared to Google at this critical stage of their respective business lives:

Based on such numbers, and on the prospect for a billion users by the end of 2012, everyone began to extrapolate and predict Facebook's dominance of the global advertising market.

Until some cracks began to appear.

The first one was General Motors' decision to pull its ads off Facebook. This was due to poor click-through performance compared to other ads vectors such as Google. No big deal in terms of revenue: according to Advertising Age, GM had spent a mere $10m (£6.8m) in FB ads and a total $30m maintaining its presence on the social network. But Facebook watchers saw it a major red flag.

The next bad signal came during the roadshow, when Facebook issued a rather stern warning about its advertising performance among mobile users.

We believe this increased usage of Facebook on mobile devices has contributed to the recent trend of our daily active users (DAUs) increasing more rapidly than the increase in the number of ads delivered.

If Facebook can't effectively monetise its mobile users, it is in serious trouble. Numbers compiled by ComScore are staggering: last March, the average American user spent 7hrs 21 minutes on mobile versions of Facebook (80% on applications, 20% on the mobile site). This represents a reach of more than 80% of mobile users and three times that of the next social media competitor (Twitter), see below:

(source : ComScore)

More broadly, Facebook experiences the unlimited supply of the internet in which users create inventory much faster than advertising can fill it. This trend is known to push ads prices further down as scarcity no longer contains them. The reason why the TV ad market is holding pretty well is its lasting ability to create a tension on prices thanks to the fixed numbers of ad slots available over a given period of time.

Unfortunately for its investors, in many ways, Facebook is not Google. First of all, it has no advertising "killer format " comparable to Google's AdWords. The search engine text ads check all the boxes that make a success: they are ultra-simple, efficient, supported by a scalable technology that makes them well-suited for the smallest advertisers as well as for the biggest ones; the system is almost friction-free thanks to an automated marketplace; and its efficiency doesn't depend on the quality of creation (there is no room for that). One cent a time, Google churns its enormous revenue stream, without any competition in its field.

By contrast, Facebook's ad system looks more traditional. For instance, it relies more on creativity than Google does. Although the term sounds a bit overstated considering the level of tactics Facebook uses to collect fans and raise "engagement" of any kind. For example, Tums, the anti-acid drug, developed a game encouraging users to throw virtual tomatoes at pictures of their friends. On a similar level of sophistication, while doing research for this column, I landed on the Facebook Studio Awards site showcasing the best ads and promotional campaigns. My vote goes to the French chicken producer Saint Sever, whose agency devised this elegantly uncomplicated concept: "1 ami = 1poulet" (one friend, one chicken):

If this is the kind of concept Facebook is proud to promote, it becomes a matter of concern for the company's ARPU.

Speaking of Average Revenue Per User, last year, Facebook made $4.34 per user in overall advertising revenue. A closer look shows differences from one market to another: North America, the most valuable market, yielded $9.51 per user versus $4.86 for the European market, $1.79 in Asia and only $1.42 for the rest of the world. Facebook's problem lies exactly there: the most profitable markets are the most saturated ones while the potential for growth resides mostly in the low-yield tier. In the meantime, infrastructure costs are roughly identical: it costs the same to serve a page, or to synchronize a photo album located in Pennsylvania or in Kazakhstan (it could even cost more per user in remote countries, and some say that FB's infrastructure running costs are likely to grow exponentially as more users generate more interactions between themselves).

Facebook might be tempted to mimic a rather questionable Google trait, that is "The Theory Of Everything". Over the last years, we've seen Google jumping on almost everything (including Motorola's mobile business), trying a large, confusing array of products and services in order to see what sticks on the wall. The end result is an impressive list of services that became very valuable to users (mail, maps, docs). But more than 90% of Google revenue still come from a single stream of business, search ads.

As for Facebook, we had a glimpse already with the Instagram acquisition (see a recent Monday Note), which looked more like a decision triggered by short-term agitation than by long-term strategic thought. We might see other moves like this as Mark Zuckerberg retains 57% of the voting shares and as the company sits on a big (more than $6bn) pile of cash. Each month brings up a new business Facebook might be tempted to enter, from mobile phones, to search.